1. Field of the Invention
The present invention relates to a seat structure, in particular relates to seats suitable for a transportation machine such as a plane, a train, a ship, a forklift, a motor vehicle and so on.
2. Description of the Related Art
A seat structure formed by stretching a cushioning member such as a solid knitted fabric (a three-dimensional net member) across a seat frame is disclosed in Patent Documents 1 to 5. When forming a cushioning member stretching across a seat frame in this manner, in order to enhance preventability of bottom-touch, vibration absorbency, impact absorbency, a base net made of cloth such as a solid knitted fabric, a two-dimensional cloth and the like is provided below the above-described cushioning member via an elastic member. In all of the Patent Documents 1 to 5, a torsion bar unit including a torsion bar, an arm biased in the falling rearward direction, and a supporting frame supported by the arm, is disposed in the rear of a seat cushion, and the base net is elastically supported by connecting the rear end of the base net to the supporting frame. Note that the front end of the base net is fixed to a front frame composing the seat frame.
[Patent Document 1] Japanese Patent Application Laid-open 2004-347577
[Patent Document 2] Japanese Patent Application Laid-open 2003-182427
[Patent Document 3] Japanese Patent Application Laid-open 2004-188164
[Patent Document 4] Japanese Patent Application Laid-open 2004-141545
[Patent Document 5] International Patent Publication WO 2004/007238A1
In the technology disclosed in Patent Documents 1 to 5, by elastically supporting a base net with a torsion bar, it is possible to achieve improvement of vibration absorbency as described above without bringing a feeling of something foreign to users despite a fact that by using thinner material compared with urethane material generally used in a prior art as a cushioning member for a car seat or the like, a hip point (H. P.) is lowered by about 10 mm compared with using the urethane. However, in all the technology described above, a torsion bar is disposed in the rear of the seat cushion, and the front end of the base net is fixed. In particular, a structure disposing arms and a supporting frame connected to a torsion bar on a rearward and upward-tilting side is excellent in vibration absorbency, but gives a feeling of the buttocks or the pelvis being pushed from behind when seating due to pulling the rear end of the base net in a rearward and upward-tilting direction, or gives a sense of so-called seating on a hammock. Then, the sense of seating on a hammock is eliminated by taking a countermeasure such as lying urethane material under the buttocks, the urethane material having a thickness of about 20 mm and being enhanced in facial rigidity by impregnating felt into the urethane. Disposition of another urethane material in the front of the seat cushion is carried out in order to reduce a feeling of something foreign of a frame (front frame) disposed in the front of the seat cushion to fix the front end of the base net, but since a material having a sense of relatively hard springiness is used as the urethane material, it sometimes lacks a sense of stroke, and on receiving force from the leg during pedal operation, the counter force is sometimes perceived as a sense of hitting the front end of the seat cushion.
In a structure disposing arms and a supporting frame connected to the torsion bar on the rear tilting-upward side, since a point of load while stably seated is under the ischium node, namely, close to the torsion bar unit disposed in the rear, a component force in the direction of gravity works on the torsion bar, which makes the torsion bar hard to move, and a component force in the horizontal direction to move the arms and the supporting frame in front and behind is hard to work. Therefore, it is possible to further enhance the vibration absorbency if such points are improved.
When a rearward moment equal to or more than the predetermined value is applied on the seat back, the seat cushion is elastically deformed downward from the rear side portion from near the center of side frames of the seat cushion. Accordingly, a supporting frame of a torsion bar unit provided in the rear of the seat cushion so that the torsion bar is positioned at the top with the arms protruding downward from the torsion bar, displaces as if being pushed out forward accompanying this deformation and works to loosen the base net. Accordingly, when the base net is disposed in this manner, it is impossible to sufficiently execute a function to control frame deformation of the seat back by the base net.
Since the structure disposing the torsion bar unit in the rear places the configuration in the vicinity of the rear portion of the seat cushion, and requires a large space to dispose the torsion bar unit, it has a problem in that the leg room available behind the front seat is often constricted.